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Burnt wire. How?

3K views 20 replies 14 participants last post by  bdesj 
#1 ·
I noticed Tuesday night that I had no headlights on my Wee. Looked into it today and found the hot connection coming out of my fuse box towards the light relays was burned to a crisp AFTER the 20A fuse, which never blew. WTF? Isn`t that the whole reason for fusing circuits? What might I have wrong here? I don`t know much about electrical troubleshooting, but I see nothing wrong with the rest of the headlight system (EB relay kit, connections, plug-ins to lamps). I did move the 2A fuse to my voltage gauge away from the headlight fuse, don`t know why I had them right next to each other when there are plenty of empty spots, but still ...

I`m trying to upload a picture directly to the website, but not sure if it will show up- have only done it previously by tying in to PhotoBucket.
 

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#3 ·
The PC-8 is rated for 20A bust not constant. What are your headlights drawing?

The screw down terminal block can create a high resistance spot if the wire has a bad connection. The resistance while create heat and burn up. Most screw down blocks of that size are only rated for 15A constant.
 
#4 ·
Thanks, Clayyalc. I have stock headlights which, as I (far from an electrical technician) calculate, total 10A continuous. I only used the 20A fuse because that`s what the guy who makes the kits shows in his sample installations. Maybe because of the "flash to pass" condition, which temporarilly draws double? Any rate, I don`t use that feature save for a few time when I have triggered it inadvertently.

Yeah, the screw connections do seem a bit chintzy to me, though I don`t know what they are rated for. On the other hand, the designer specifically shows my setup on his website and other riders are apparently using the same setup with no problems.

The screw down terminal block can create a high resistance spot if the wire has a bad connection. The resistance while create heat and burn up.
It sounds like you saying that I might not have made a good connection. It`s tough to get much more torque on those tiny little screws, but maybe I did not have enough? Also a little challenging to get all the strands stuffed into the box. Is there some kind of crimp I can put on the wire end and then screw into the fusebox connector?
 
#6 ·
Whatever the cure, I think you`re right about the bad connection being the root cause. I ran out of time yesterday before I could test for shorts downstream, but I`ll do that over the weekend to be sure. Watched a YouTube video about the ferrules that you suggest and they look like a good idea. Alternatively, I wonder if tinning the ends of the wire might be a good measure? Curious as to how other people have run headlights through a PC-8 and how it has been doing for them.
 
#9 · (Edited)
High resistance and high current don't go together well.

Fuse won't open if current is lower than fuse rating. 20A seems pretty huge for that small terminal block though. Cut it off and use another spot.

If you had a IR camera and saw how hot it gets you really could have known. :wink2:
 
#11 ·
Most likely the screw terminal worked itself loose. What size wiring is it? Did the PC8 come with a 20A fuse?

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#13 ·
Most likely the screw terminal worked itself loose. What size wiring is it? Did the PC8 come with a 20A fuse?

Sent from my SM-T700 using Tapatalk
This would be my first thought as well. Motorcycles vibrate a lot. Vibra-TITE VC-3 is a non-hardening thread locker that might help if they start to loosen up again. I have used it for mixture jets on carbs for small 2-cycle engines (weedwacker / scooter). Helps to dampen the vibrations and hold the threads a bit, while still allowing for future adjustments.
 
#14 ·
Crimped connections using terminals are best for high-vibration environments, preferably with some sort of strain relief like at least a wire tie to a fixed point a couple of inches away from the termination point. Solder generally isn't good because the joints can crack from vibration or a wire can vibrate and start severing strands just behind the solder joint/tinning. If you're going to go about it with cheap crimpers at least give the wire a good pull test before putting into use so that you know you have a tight crimp.

If you get a loose connection it can cause an increase in current in the circuit due to the voltage drop across the loose connection and a corresponding increase in wire temperature. Headlights will try and pull the wattage they need and if the voltage to the bulbs is reduced the current will go up to meet the power demand of the bulbs (Ohms Law: Power in Watts = Voltage x Current).
 
#15 ·
Do you have the Eastern Beaver Headlight relay kit installed? I am not sure about your bike, but Suzuki runs the starter and headlights via the same wiring with no relays. This could (over time) cause issues and is why many Strom owners install the H4 relay.
 
#16 ·
P (watts) = RxI^2 or VxI

The picture indicates that the fault was at the terminal block. As others have noted you most likely had a resistive connection at this point, which creates a localized heat source. If the wire gauge was too small the burn wouldn't have been localized. If the current (I) was too high the fuse would have blown (assuming correct sizing).
In any case, it's a bummer.
 
#21 ·
Checking regularly sounds like a dang good idea. Then again, locating the fuse box behind the fairing sounded like a dang good idea too, and that`s the one I wet with. The two don`t really mesh well together!

I have the same set up but did not use the PC8 for the headlights. Left them on the battery. I just use it for accessories.
In hindsight, that doesn`t sound like a bad plan either. The world is full of options, damnit! Everybody park an upturned red flower pot on your head and sing along... "Freedom of choice is what we got, freedom from choice is what we want..."
 
#20 ·
I have the same set up but did not use the PC8 for the headlights. Left them on the battery. I just use it for accessories. I also did not fasten the PC8 to anything on the bike under the seat. I set it on a rag in the plastic box under the seat. Less vibrations for it that way?
 
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